Optical Fingerprint Sensor with Enhanced Anti-Counterfeiting Features

ABSTRACT

An image sensing apparatus is disclosed. The image sensing apparatus includes a pixel array and micro lenses disposed above the pixel array. The pixel array includes sensing pixels configured to capture minutia points of a fingerprint and positioning pixels configured to provide positioning codes.

PRIORITY DATA

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 63/389,292, filed on Jul. 14, 2022, and U.S. Provisional PatentApplication Ser. No. 63/382,143, filed on Nov. 3, 2022, the entiredisclosures of which are incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. For example, there is considerableinterest in providing consumer and/or portable electronic devices (e.g.,smart phones, electronic tablets, wearable devices, and so on) withfingerprint sensing applications (e.g., optical sensors for fingerprintrecognition) inside limited device housing without compromising securitylevel provided by fingerprint sensing applications.

In some fingerprint sensing applications, fingerprint grayscale levelimages are sensed by pixels of an optical fingerprint sensor that canonly sense grayscale level images (i.e., cannot sense color images).Further, such grayscale level images do not include any specialpositioning codes or patterns. Such fingerprint sensing applications aresusceptible to counterfeiting. Therefore, conventional means of opticalfingerprint sensors are not satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 illustrates an electronic device with a fingerprint sensingregion on surface space, according to various aspects of the presentdisclosure.

FIG. 2 is a cross-sectional view of an electronic device integrated withan optical fingerprint sensor under a display panel, according tovarious aspects of the present disclosure.

FIG. 3 is a cross-sectional view of an embodiment of the opticalfingerprint sensor as shown in FIG. 2 , according to various aspects ofthe present disclosure.

FIGS. 4A, 4B, and 4C are top views of a pixel array with positioningpixels overlaid with fingerprint images at different stages offingerprint recognition, according to various aspects of the presentdisclosure.

FIGS. 5, 6, and 7 illustrate embodiments of the distribution ofpositioning pixels in a pixel array, according to various aspects of thepresent disclosure.

FIGS. 8A, 8B, 8C, 8D, 8E, 8F, and 8G illustrate embodiments of thedistribution of positioning pixels and color pixels in a pixel array,according to various aspects of the present disclosure.

FIG. 9 illustrates a flowchart of a method for fingerprint recognition,according to various aspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations beyond the extentnoted.

Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

The present disclosure is generally related to designs and methods forfingerprint sensing, such as in anti-counterfeiting applications whichutilize optical fingerprint sensor (abbreviated as OFPS). Moreparticularly, some embodiments are related to integrating specialpatterns of positioning pixels (also referred to as positioning codes)and/or extra color pixels for adding skin tone codes to an OFPS forenhancing anti-counterfeiting capabilities of an OFPS.

OFPS is one approach of biometric sensing that draws considerableinterest to provide security features to electronic devices, and moreparticularly, consumer and/or portable electronic devices (e.g., smartphones, electronic tablets, wearable devices, and so on). An OFPS-basedfingerprint recognition (or fingerprint sensing) system is based onunique features of a user and may not rely on memorization or the use ofother input devices by the user, such as password input. An OFPS-basedfingerprint recognition system also provides the advantage of beingdifficult to hack for the same reason.

Among various biometric sensing techniques, fingerprint recognition is areliable and widely used technique for personal identification orverification. A fingerprint recognition system generally includesfingerprint sensing and matching functionalities, such as collectingfingerprint images and comparing those images against known fingerprintinformation. In particular, one approach to fingerprint recognitioninvolves scanning a reference fingerprint and storing the referenceimage acquired. The characteristics of a new fingerprint may be scannedand compared to the reference image already stored in a database todetermine proper identification of a person, such as for verificationpurposes. A fingerprint recognition system may be particularlyadvantageous for authentication in consumer and/or portable electronicdevices. For example, an optical sensor for acquiring fingerprint imagesmay be carried inside the housing of an electronic device.

The effectiveness of biometric security systems may be affected by theaccuracy with which the unique biometric data is able to be detected. Inthe case of fingerprint recognition systems, this means improvingaccuracy when comparing an acquired fingerprint image to a referencefingerprint image stored in a database. What is stored in a database asa representation of a reference fingerprint image is often a collectionof minutia points representing ridges and valleys of a fingerprint. Sucha collection of minutia points is also referred to as a minutia map. Ifa minutia map is hacked or leaked, the fingerprint image can be rebuiltby reserve engineering. The security provided by a fingerprintrecognition system is thus compromised. In some embodiments of thepresent disclosure, positioning pixels are added to a pixel array of anOFPS to add additional codes to a minutia map. Such codes are referredto as fingerprint positioning codes or position reference codes. Thefingerprint positioning codes turns a direct recordation of minutiapoints of where ridges and valleys locate to vectors representingrelative locations of minutia points with respect to positioning pixels.Thus, even a minutia map is hacked or leaked, without knowledge ofdistributions of positioning pixels and how the positioning pixels arereferenced to, a fingerprint image still cannot be rebuilt from theminutia map. Thus, adding positioning codes enhances anti-counterfeitingcapability of an OFPS.

Further, in some fingerprint sensing applications, fingerprint grayscalelevel images are sensed by image sensing pixels (abbreviated as pixels)that can only sense the grayscale level image (i.e., cannot sense colorimages). Such pixels are referred to as grayscale pixels or “W” pixels.For example, monochromatic image sensors are often adapted as pixels forfingerprint recognition applications, which produces grayscale levelimages. In some embodiments of the present disclosure, one or more colorimage sensors are added to the pixel array as color pixels (RGB),thereby adding fingerprint color codes representing skin tones to thereference and acquired fingerprint images. The fingerprint color codesfurther enhance anti-counterfeiting capability of an OFPS. In variousembodiments, positioning pixels producing fingerprint positioning codesand color pixels producing fingerprint color codes may be independentlyor jointly applied to a pixel array of an OFPS. For example, an OFPS mayinclude a pixel array with some grayscale pixels replaced by positioningpixels, a pixel array with some grayscale pixels replaced by colorpixels, a pixel array with some grayscale pixels replaced by positioningpixels and some grayscale pixels replaced by color pixels, or even apixel array with no grayscale pixels but a combination of color pixelsand positioning pixels.

FIG. 1 illustrates an electronic device 100 with a fingerprint sensingregion on surface space, in accordance with some embodiments of thepresent disclosure. As shown in FIG. 1 , the electronic device 100 isillustratively a mobile wireless communication device (e.g., a smartphone). In other embodiments, the electronic device 100 may be any othersuitable electronic device, such as a laptop computer, an electronictablet, a portable gaming device, a navigation device, or a wearabledevice. The electronic device 100 includes a housing 102 together withother components, such as processor(s) and memories, inside the housing102. A display panel 104 is carried by the housing 102. In theillustrated embodiment, the display panel 104 is an organiclight-emitting diode (OLED) display panel. In various embodiments, thedisplay panel 104 may be any other suitable type display panel, as willbe appreciated by those skilled in the art, such as liquid-crystaldisplay (LCD) panel, light-emitting diode (LED) display panel, oractive-matrix organic light-emitting diode (AMOLED) display panel.

In the illustrated embodiment, the display panel 104 expandssubstantially to the entire surface space of the electronic device 100.Some margins between the display panel 104 and edges of the housing 102may be left for bezel panels 106. The display panel 104 stacks aboveimage sensing features for fingerprint detection, or other suitablebiometric sensing features. The image sensing features will be describedfurther in details later. The display panel 104 acts as both a displayand an input device through which the image sensing features acquiresfingerprint images. As such, the display panel 104 performs multipledevice functions in response to user input. For example, the displaypanel 104 may first display a prompt (e.g., a finger icon or aninstruction text) on screen when the electronic device 100 is in a lockstatus. The display panel 104 may further highlight a sensing region108. When a user's finger 110 is placed inside the sensing region 108,in either near field or in direct contact with the display panel 104,the image sensing features are activated and acquire a fingerprint imagefrom the user's finger 110. Such acquired fingerprint image (biometricdata) is sent to processor(s) for matching and/or spoof detection. Ifthe acquired fingerprint image matches a reference fingerprint imagestored in memories, the electronic device 100 may thereafter transitinto an unlock status, and the display panel 104 starts to show desktopicons or response to various other user inputs. The display panel 104may further integrate with touch sensor arrays. In such case, thedisplay panel 104 is also a touch display panel.

FIG. 2 is a cross-sectional view of a portion of the electronic device100. This portion of the electronic device 100 carries the fingerprintrecognition function and can be regarded as a fingerprint recognitionsystem 200. The fingerprint recognition system 200 is in a stack-upconfiguration, including a display panel 202 on the top, a lightconditioning layer 204 in the middle, and an OFPS 206 at the bottom. Thedisplay panel 202 illuminates the sensing region 108 above. When lightemitted from the display panel 202 is reflected from the user's finger110, the reflected light travels downwardly through the display panel202 and the light conditioning layer 204 and eventually arrives at theOFPS 206. In one embodiment, the image OFPS 206 includes an array ofoptical sensing elements 207, such as complementary metal oxidesemiconductor (CMOS) image sensors and/or charged coupled device (CCD)sensors. The optical sensing elements 207 are capable of detectingintensities of the incident light. The OFPS 206 thereby convers theincident light into a pixel image, which includes biometriccharacteristics of the user's finger 110. Each pixel of the pixel imagemay correspond to intensity of the incident light recorded at acorresponding location of an optical sensing element 207.

In some embodiments, the display panel 202 includes a cover glass 214(or cover lens) that protects inner components of the electronic device100. The sensing region 108 is defined above the cover glass 214. A topsurface 216 of the cover glass 214 forms a sensing surface, whichprovides a contact area for the user's finger 110 or other suitableobjects. Inside the sensing region 108, the user's finger 110 maydirectly touch the top surface 216 or keep a small distance away fromthe top surface 216 as during a near field sensing. The cover glass 214may be made of glass, transparent polymeric materials, or other suitablematerials.

The display panel 202 includes an illumination layer or display layer220 under the cover glass 214. The display layer 220 includes an arrayof light emitting pixels 222. Different light emitting pixels 222 may beconfigured to emit different colors, such as the ones emitting redlight, the ones emitting green light, or the ones emitting blue light.Due to geometry relationships with the sensing region 108, the lightemitting pixels 222 can be categorized into two groups, one groupdirectly under the sensing region 108 and another group outside of thesensing region 108. The light emitting pixels 222 outside of the sensingregion 108 perform regular display functions, while the light emittingpixels 222 directly under the sensing region 108 perform both regulardisplay functions and illumination function during biometric sensing,depending on applications. In various embodiments, pixel distance D1between adjacent light emitting pixels 222 is in a range from about 5micrometers to about 30 micrometers, where other values and ranges arewithin the scope of this disclosure. In a specific example, the pixeldistance D1 may be in a range from about 10 micrometers to about 20micrometers.

In some embodiments, the display panel 202 further includes a blockinglayer 224. The blocking layer 224 is a semitransparent or opaque layerthat may be disposed below the display layer 220. Outside of the sensingregion 108, the blocking layer 224 is continuous, obscuring componentsunder the display layer 220 from the light emitted by the light emittingpixels 222 and from ambient light. Directly under the sensing region108, the blocking layer 224 has a plurality of openings 226. Eachopening 226 locates between two adjacent light emitting pixels 222. Theopenings 226 allow the light reflected from the sensing region 108 totravel through. In the illustrated embodiment, there is one opening 226located between two adjacent light emitting pixels 222. The opening 226may have a width (or diameter) D2 in a ratio to the pixel distance D1from about 40% to about 90%, where other values and ranges are withinthe scope of this disclosure. In some other embodiments, there are twoor more openings 226 located between two adjacent light emitting pixels222. The opening 226 may thus have a width (or diameter) D2 in a ratioto the pixel distance D1 from about 20% to about 40%.

In various embodiments, the display layer 220 may be an LCD display(using backlight with color filters to form RGB pixels), a LED display(e.g., a microLED, in which the pixel material can be inorganic materialused in LED), an OLED display, or any other suitable displays. In theillustrated embodiment, the light emitting pixels 222 are organic lightemitting diodes (OLED) and the display layer 220 is an OLED display.Examples of an OLED display may include active-matrix OLED (AMOLED),passive-matrix OLED (PMOLED), white OLED (WOLED), and RBG-OLED, and/orother suitable types of OLED. An OLED display is usually thinner,lighter, and more flexible than other types of displays, such as LCD orLED displays. OLED display does not require a back light, since thelight can be generated from the organic light emitting material in anOLED, which allows a pixel to be turned completely off. The organiclight emitting material can be an organic polymer, such aspolyphenylenevinylene and polyfluorene. Due to the organic lightemitting material producing its own light, the OLED display can alsohave a wider viewing angle. This can be in comparison to an LCD display,which works by blocking light that can lead to obstruction of certainviewing angles.

The OLED diodes emit light using a process called electroluminescence,which is a phenomenon where the organic light emitting material can emitlight in response to an electric current passing through. In someexamples, the OLED diodes can include hole injection layers, holetransport layers, electron injection layers, emissive layers, andelectron transport layers. The color of light emitted by an OLED diodedepends on the type of organic light emitting material used in theemissive layer. Different colors can be obtained with a variety ofchemical structures of the organic light emitting material. Theintensity of light can depend on the number of emitted photons or thevoltage applied on the OLED diodes. In some embodiments, each lightemitting pixel is formed with the same organic light emitting materialthat generates white light, but further includes a red, green, or bluecolor filter to filter out colors other than the target color,respectively. The color filter can be formed using a cholesteric filtermaterial such as a multilayer dielectric stack that includes materialswith different indices of refraction configured to form an opticalfilter.

As shown in FIG. 2 , under the sensing region 108, the lightconditioning layer 204 is stacked under the display panel 202. The lightconditioning layer 204 includes a semiconductor layer 240 and an opticalfiltering film 242. In one embodiment, the semiconductor layer 240comprises a silicon microelectromechanical systems (MEMS) structure. Forexample, the semiconductor layer 240 comprises a collimator 245including an array of apertures 246. Each aperture 246 is directly aboveone or more optical sensing elements 207 in the OFPS 206. The array ofapertures 246 may be formed by any suitable techniques, such as plasmaetching, laser drilling, or the like. The array of apertures 246conditions incident light reflected from the sensing region 108. Withthe OFPS 206 stacked at the bottom, the display panel 202, especiallythe relative thick cover glass 214, adds extra vertical distance betweenthe user's finger 110 and the OFPS 206, which causes stray light fromnearby regions of the user's finger 110 also arrives an optical sensingelement 207 together with the light from a small spot directly above.The stray light contributes to image blurring. The array of apertures246 helps filtering out the stray light and substantially only allowsthe light from the small spot directly above to be detected, resultingin sharper images.

A metric of the collimator 245 is an aspect ratio of the aperture 246,defined as the height (a) divided by the diameter (e) of the aperture246. The aspect ratio of the aperture 246 is sufficiently large to allowlight rays at normal or near normal incidence to the collimator 245 topass and reach the optical sensing element 207. Examples of suitableaspect ratio of the aperture 246 are ranging from about 5:1 to about50:1 and sometimes ranging from about 10:1 to about 15:1. Other valuesand ranges are within the scope of this disclosure. In an embodiment,the height (a) of the aperture 246 is in a range from about 30micrometers to 300 micrometers, such as about 150 micrometers. Invarious embodiments, the collimator 245 may be an opaque layer witharray of holes. In some embodiments, the collimator 245 is a monolithicsemiconductor layer, such as a silicon layer. Other examples of thecollimator 245 may include plastics such as polycarbonate, PET,polyimide, carbon black, inorganic insulating or metallic materials, orSU-8.

As shown in FIG. 2 , the light conditioning layer 204 also includes theoptical filtering film 242 above the semiconductor layer 240. Theoptical filtering film 242 selectively absorbs or reflects certainspectrums of incident light, especially components from the ambientlight 250, such as infrared light and/or a portion of other visiblelight (e.g., red light). The optical filtering film 242 helps reducingthe optical sensing element 207's sensitivity to ambient light 250 andincreasing its sensitivity to the light emitted from the light emittingpixels 222. The optical filtering film 242 may extend continuously anddirectly above the collimator 245, and have an opening 260 outside ofthe collimator 245.

In an example, the optical filtering film 242 may include a thin metallayer or a metal oxide layer that absorbs or reflects light in certainspectrums. In another example, the optical filtering film 242 mayinclude dye(s) and/or pigment(s) that absorb or reflect certain lightcomponents. Alternatively, the optical filtering film 242 may includeseveral sub-layers or nano-sized features designed to cause interferencewith certain wavelengths of incident light. In one embodiment, theoptical filtering film 242 may include one or more materials like asilicon oxide, a titanium oxide, or another metal oxide.

The optical filtering film 242 may be deposited on a dielectric layer241, which may be a buried oxide layer on the semiconductor layer 240.In one embodiment, the buried oxide layer 241 may include one or morematerials like a thermal oxide, a plasma enhanced oxide (PEOX), ahigh-density-plasma (HDP) oxide, etc. In addition, the lightconditioning layer 204 also includes a passive oxide layer 255 below thesemiconductor layer 240. In one embodiment, the passive oxide layer 255may include one or more materials like a PEOX, a HDP oxide, etc.

The OFPS 206 in this example includes a substrate 268, a plurality ofoptical sensing elements 207 in the substrate 268, and bond pads 264 inthe substrate 268. Each bond pad may be a metal pad including conductivematerial. As shown in FIG. 2 , the stack of the passive oxide layer 255,the semiconductor layer 240, the buried oxide layer 241 and the opticalfiltering film 242 may further have a few openings 260. The openings 260allow some conductive features, e.g. bond wires 262, to interconnect atleast one of the bond pads 264 on the top surface of the image sensinglayer 206 to external circuits, such as a processor of the electronicdevice 100. The bond pads 264 route to control signal lines andpower/ground lines embedded in the image sensing layer 206. The imagesensing layer 206 may further include alignment marks for alignmentcontrol during fabrication and assembly. In other embodiments, thealignment marks are located at the passive oxide layer 255 or ametal/bond pad layer of the image sensing layer 206 for alignmentcontrol during fabrication and assembly.

In one embodiment, the semiconductor layer 240 has a thickness (a) ofabout 50 to 200 micrometers. In one embodiment, the passive oxide layer255 has a thickness (b) of about 400 to 2000 nanometers. In oneembodiment, the buried oxide layer 241 has a thickness (c) of about 1000to 2000 nanometers. In one embodiment, the optical filtering film 242has a thickness (d) of about 1 to 5 micrometers. In one embodiment, eachaperture 246 of the collimator 245 has a diameter of about 5 to 30micrometers. According to various embodiments, the openings 260 of thepassive oxide layer 255, the semiconductor layer 240 and the buriedoxide layer 241 have different diameters. For example, the opening ofthe buried oxide layer 241 has a diameter (f) of about 100 to 140micrometers; the opening of the semiconductor layer 240 has a diameter(g) of about 80 to 120 micrometers; and the opening of the passive oxidelayer 255 has a diameter (h) of about 60 to 100 micrometers.

In one embodiment, a method for capturing a fingerprint image from auser's finger illuminated by a display panel integrated with a lightconditioning layer is described below. The screen of the electronicdevice 100 may be first in a lock status. A prompt is displayed, wherethe prompt may be an icon, such as a fingerprint icon or an instructiontext, which highlights a sensing region 108 on the screen. The prompt isshown by light emitting pixels 222 under the sensing region 108. Thelight emitting pixels 222 can be OLED diodes. The light emitting pixels222 outside of the sensing region 108 may be turned off in the lockstatus or display preset screen saver images. Then, when the user'sfinger 110 stays steady in the sensing region 108 for more than apredetermined time, such as the user holding a finger steady for aboutone hundred milliseconds, a biometric detection mode begins. Otherwise,the method goes back to wait for a new user input.

In the biometric detection mode, the prompt shown on the screen isturned off and the light emitting pixels 222 under the sensing region208 start to illuminate the user's finger 110. The light 270 emittedfrom the light emitting pixels 222 can travel through the cover glass214 and arrives at the user's finger 110. The user's finger 110 caninclude ridges 272 and valleys 274. The ridges 272 of the finger canreflect more light due to a closer distance to the top surface 216 thanthe valleys 274, and the valleys 274 can reflect less light. The light270 is in turn reflected back towards the light conditioning layer 204.

Then, the optical filtering film 242 filters certain spectrums of light.In some embodiments, the optical filtering film 242 is an infrared lightcut-off filter, which filters (or reduces) infrared light component fromthe incident light, such as by absorbing or reflecting. The ambientlight 250, such as sunlight, is the major source of infrared light. Theinfrared light may easily penetrate the user's finger 110. Thus theinfrared light does not carry useful information of biometriccharacteristics of the finger and can be considered as part of thenoise. Blending the infrared light component from the ambient light withthe reflected light from the light emitting pixels reduces thesensitivity of the optical sensing elements 207. By filtering theinfrared light before sensing, signal-notice-ratio (SNR) of the incidentlight will be increased. In some other embodiments, the opticalfiltering film 242 may target light in certain spectrums other thaninfrared light, for example, red light in the visible spectrum orultra-violet light. The light filtering profile of the optical filteringfilm 242 may be formulated to give a particular appearance of color,texture, or reflective quality thereby allowing for optimized filteringperformance. In some embodiments, the optical filtering film 242 is aninfrared light cut-off filter and there is a separate film stacked underor above for filtering red light to reduce ghost image.

Then the collimator 245 filters stray light components in the light 270.With high aspect ratio of the apertures 246, the collimator 245 onlyallows light rays reflected from the sensing region 108 at normal ornear normal incidence to the collimator 245 to pass and eventually reachthe OFPS 206. The optical sensing element 207 can be used to measure theintensity of light and convert the measured intensity into pixel imageof the input object, such as the user's finger 110. On the other hand,stray light with a larger angle from normal, strike the collimator 245,either on its top surface or at surface within the apertures 246 (e.g.,aperture sidewalls) and are blocked and prevented from reaching theimage sensing layer 206 below. The aspect ratio of the apertures 246 issufficiently large to prevent stray light from traveling through thecollimator 245, such as from about 5:1 to about 50:1.

The OFPS 206 then acquires a fingerprint image. The optical sensingelements 207 inside the image sensing layer 206 can convert the incidentlight into electrical outputs. Each optical sensing element 207's outputmay correspond to one pixel in the fingerprint image. The opticalsensing elements 207 may comprise monochromatic image sensors (grayscalepixels) and/or color image sensors (color pixels). In some embodiments,each of the optical sensing elements 207 may be configured to correspondwith specific light wavelengths, such as a sensor element directly undera red light emitting pixel 222 for sensing a red light wavelength, asensor element directly under a green light emitting pixel 222 forsensing a green light wavelength, and a sensor element directly under ablue light emitting pixel 222 for sensing a blue light wavelength.

The acquired fingerprint image is compared with an authentic referenceimage previously stored in a memory (or database). If the fingerprintimages match, the screen is unlocked. The light emitting pixels 222under the sensing region 108 will stop illumination and join the otherlight emitting pixels 222 outside of the sensing region 108 to startdisplay regular desktop icons as in an unlock status. If the fingerprintimages do not match, the method goes back to wait for new biometricdetection.

With reference to FIG. 3 , a cross-sectional view of some embodiments ofa semiconductor structure for an OFPS 300 is provided. The OFPS 300 maybe substantially similar to the OFPS 206 discussed above with referenceto FIG. 2 . The OFPS 300 includes a pixel array 336 of image sensingpixels (abbreviated as pixels) 302 arranged in rows and columns. Forexample, the pixel array may include about 3 million pixels 302 arrangedin 1536 rows and 2048 columns. The semiconductor structure includes asemiconductor substrate 304 within which photodiodes 306 correspondingto the pixels 302 are arranged. The photodiodes 306 are arranged in rowsand/or columns within the semiconductor substrate 304, and configured toaccumulate charge (e.g., electrons) from photons incident on thephotodiodes 306. The semiconductor substrate 304 may be, for example, abulk semiconductor substrate, such as a bulk silicon substrate, or asilicon-on-insulator (SOI) substrate.

A DTI region 308 defines a substrate isolation grid, made up of gridsegments, such as individual rectangles or squares which abut oneanother. Further, the DTI region 308 extends into the semiconductorsubstrate 304 from about even with an upper surface of the substrate304. The DTI region 308 is laterally arranged around and between thephotodiodes 306 to advantageously provide optical isolation betweenneighboring photodiodes 306. The DTI region 308 may be, for example, ametal, such as tungsten, copper, or aluminum copper. Alternatively, theDTI region 308 may be, for example, a low-n material. A low-n materialhas a refractive index less than light filters 310 overlyingcorresponding ones of the pixels 302. The light filters 310 may be colorfilters for color pixels, transparent filters for monochromatic pixels(grayscale pixels), or a combination of color filters and transparentfilters. In some embodiments, the DTI region 308 has a refractive indexless than about 1.6. Further, in some embodiments, the DTI region 308 isa dielectric, such as an oxide (e.g., SiO₂) or hafnium oxide (e.g.,HfO₂), or a material with a refractive index less than silicon.

An antireflective coating (ARC) 316, and/or a first dielectric layer318, of the semiconductor structure are arranged over the semiconductorsubstrate 304 along an upper surface of the semiconductor substrate 304.In embodiments where both the ARC 316 and the first dielectric layer 318are present, the first dielectric layer 318 is typically arranged overthe ARC 316. The ARC 316 and/or the first dielectric layer 318 space thesemiconductor substrate 304 from a composite grid 320 of thesemiconductor structure that overlays the substrate 304. The firstdielectric layer 318 may be, for example, an oxide, such as silicondioxide.

The composite grid 320 is laterally arranged around and between thephotodiodes 306 to define openings within which the light filters 310are arranged. The openings correspond to the pixels 302 and arecentrally aligned with the photodiodes 306 of the corresponding pixels302. The composite grid 120 includes one or more of a metal grid 324, alow-n grid 326, and a hard mask grid 328 stacked in that order over thesemiconductor substrate 304. Each grid 324, 326, 328 is made up of gridsegments, such as individual rectangles or squares which abut oneanother to collectively make up the grid 324, 326, 328 and whichsurround respective photodiodes 306. Each grid 324, 326, 328 alsoincludes openings between the grid segments and which overlie thephotodiodes 306. The metal grid 324 blocks light from passing betweenneighboring pixels 302 to help reduce cross talk. The metal grid 324 maybe, for example, tungsten, copper, or aluminum copper. The low-n grid326 is a transparent material with a refractive index less than arefractive index of the light filters 310. Due to the low refractiveindex, the low-n grid 326 serves as a light guide to direct light to thelight filters 310 and to effectively increase the size of the lightfilters 310. Further, due to the low refractive index, the low-n grid326 serves to provide optical isolation between neighboring pixels 302.Light within the light filters 310 that strikes the boundary with thelow-n grid 326 typically undergoes total internal reflection due to therefractive indexes. In some embodiments, the low-n grid 326 is adielectric, such as an oxide (e.g., SiO₂) or hafnium oxide (e.g., HfO₂),or a material with a refractive index less than silicon. The hard maskgrid 328 may be, for example, silicon nitride or silicon oxynitride.

The light filters 310 are arranged over the ARC 316 and/or the firstdielectric layer 318. Further, the light filters 310 are arranged overthe photodiodes 306 of corresponding pixels 302 within the openings ofthe composite grid 320. The light filters 310 have upper surfaces thatare approximately even with an upper surface of the composite grid 320.Further, for color filters among the light filters 310, the lightfilters 310 are assigned corresponding colors or wavelengths of light,and configured to filter out all but the assigned colors or wavelengthsof light. Typically, the color filter assignments alternate between red,green, and blue light, such that the color filters include red colorfilters, green color filters, and blue color filters. In someembodiments, the color filter assignments alternative between red,green, and blue light according to a Bayer filter mosaic. A pixel 302corresponding to a red color filter is denoted as a red (“R”) pixel; apixel 302 corresponding to a blue color filter is denoted as a blue(“B”) pixel; a pixel 302 corresponding to a green color filter isdenoted as a green (“G”) pixel; a pixel 302 corresponding to atransparent filter is denoted as a grayscale (“W”) pixel. These pixelsare configured for light sensing and also denoted as sensing pixels302S. Besides the sensing pixels 302S for light sensing function, thereare special pixels distributed in the pixel array not for light sensingbut for providing positioning codes, denoted as positioning pixels 302P.Bottom surface of the openings of the composite grid 320 correspondingto the positioning pixels 302P is covered by opaque films 330. In someembodiments, the opaque films 330 have the same material composition asthe metal grid 324, forming a continuous metal layer blocking incidentlight. In some embodiments, the opaque films 330 are formed ofsemiconductor or dielectric material. With the opaque films 330, thephotodiodes 306 of corresponding positioning pixels 302P are not capableof sensing light, and the output from positioning pixels 302P is aboutzero (i.e., dark pixels in a fingerprint image).

A second dielectric layer 330 lining the composite grid 320 spaces thelight filters 310 from the composite grid 320, and micro lenses 332corresponding to the pixels 302 cover the light filters 310. The seconddielectric layer 130 may be, for example, an oxide, such as silicondioxide, and may be the same material or a different material than thelow-n grid 326. The micro lenses 332 are centered with the photodiodes306 of the corresponding pixels 302, and are typically symmetrical aboutvertical axes centered on the photodiodes 306. Further, the micro lenses132 typically overhang the composite grid 320 around the openings soneighboring edges of the micro lenses 332 abut. The depicted embodimentshows micro lenses 332 also above the photodiodes 306 of the positioningpixels 302P. Yet in some embodiments, there may be no micro lenses 332above the photodiodes 306 of the positioning pixels 302P.

The integrated circuit 338 includes the semiconductor substrate 304 anda device region (partially shown). The device region is arranged along alower surface of the semiconductor substrate 304, and extends into thesemiconductor substrate 304. The device region includes photodiodes 306corresponding to the pixels 302 and logic devices, such as transistors,for readout of the photodiodes 306. The photodiodes 306 are arranged inrows and columns within the semiconductor substrate 304, and configuredto accumulate charge from photons incident on the photodiodes 306.Further, the photodiodes 106 are optically isolated from each other bythe DTI region 308 in the semiconductor substrate 304, thereby reducingcross talk.

A back-end-of-line (BEOL) metallization stack 340 of the integratedcircuit 338 underlies the semiconductor substrate 304 and includes aplurality of metallization layers 342, 344 stacked within an interlayerdielectric (ILD) layer 346. One or more contacts 348 of the BEOLmetallization stack 340 extend from a metallization layer 344 to thedevice region. Further, one or more first vias 350 of the BEOLmetallization stack 340 extend between the metallization layers 342, 344to interconnect the metallization layers 342, 344. The ILD layer 146 maybe, for example, a low κ dielectric (i.e., a dielectric with adielectric constant less than about 3.9) or an oxide. The metallizationlayers 342, 344, the contacts 348, and the first vias 350 may be, forexample, a metal, such as copper or aluminum.

A carrier substrate 352 underlies the integrated circuit 338 between theintegrated circuit 338 and a ball grid array (BGA) 354. The BGA 354includes a redistribution layer (RDL) 356 arranged along a lower surfaceof the carrier substrate 352 and electrically coupled to themetallization layers 342, 344 of the BEOL metallization stack 340through one or more second, through silicon vias 358 extending throughthe carrier substrate 352. The RDL 356 is covered by a BGA dielectriclayer 360, and under bump metallization (UBM) layers 362 extend throughthe BGA dielectric layer 360 to electrically couple solder balls 364underlying the UBM layers 362 to the RDL 356. The BGA dielectric layer360 may be, for example, an epoxy. The RDL 356, the UBM layers 362, thesecond vias 358, and the solder balls 364 may be, for example, metals,such as copper, aluminum, and tungsten. Bond pads may also be providedon the upper surface of the OFPS 300, such as the bond pads 264discussed above with reference to FIG. 2 .

To illustrate the function of positioning pixels in a pixel array, FIGS.4A-4C show top views of a pixel array 400 of an OFPS at different stagesof fingerprint recognition. The pixel array 400 may be substantiallysimilar to the pixel array 336 discussed above with reference to FIG. 3. The pixel array 400 includes pixels 402 arranged in rows and columns.The pixels 402 includes sensing pixels 402S and positioning pixels 402P.The sensing pixels 402S may all be grayscale pixels, color pixels, or acombination thereof. Four positioning pixels 402P are illustrated,including a first positioning pixel 402P-a and a second positioningpixel 402P-b. Although any number of positioning pixels may present inthe pixel array 400. Fingerprint images acquired by the pixel array 400are overlaid. The sensing pixels 402S capture the light intensityvariation due to ridges and valleys of a fingerprint and generate thefingerprint image. In the illustrated embodiment, the sensing pixels402S are all grayscale pixels, and the fingerprint images are grayscalelevel images. Since the photodiodes of the positing pixels 402P areshielded by an opaque film, no light intensity is sensed at thelocations of the positioning pixels 402P. On the fingerprint images,black spots (dark pixels) appear at the locations of the positioningpixels 402P.

With reference to FIG. 4A, an initial fingerprint image is acquired asthe reference fingerprint image and stored in a memory (or database).Characteristics (minutia points) of the fingerprint are positioned withreference to positioning pixels in the form of vectors. FIG. 4Aillustrates a first vector Va, which marks a first minutia point locatedat a first location at one of the ridge lines with reference to thefirst positioning pixel 402P-a, and a second vector Vb, which makes asecond minutia point at a second location at another one of the ridgelines with reference to the second positioning pixel 402P-b. Thereference fingerprint image with the vectors referenced to positioningpixels are recorded.

With reference to FIG. 4B, a new fingerprint image is acquired when theuser's identify needs to be verified. The user's finger may not land onthe exact same location as last time, and the acquired fingerprint imagemay be shifted with respect to the reference fingerprint image.Characteristics (minutia points) of the acquired fingerprint arepositioned again with reference to positioning pixels in the form ofvectors. FIG. 4B illustrates a third vector Va′, which marks the samefirst minutia point as in FIG. 4A but shifted with reference to thefirst positioning pixel 402P-a, and a fourth vector Vb′, which marks thesame second minutia point as in FIG. 4A but shifted with reference tothe second positioning pixel 402P-b.

With reference to FIG. 4C, the acquired fingerprint image is compared tothe reference fingerprint image stored in the memory. Instead of adirection comparison of the collection of characteristics (minutia map)of the fingerprints, which is easier to be counterfeited, it is thevectors to be compared. For example, the third vector Va′ is compared tothe first vector Va, and a shift ΔVa in the form of vector iscalculated. The fourth vector Vb′ is compared to the second vector Vb,and a shift ΔVb in the form of vector is calculated. Then, the shift ΔVais compared to the shift ΔVb. The shift ΔVa should be equal to the shiftΔVb (as well as many other vectors not iterated herein) to conclude amatch.

FIGS. 5-7 illustrate various embodiments of the distribution ofpositioning pixels 402P in the pixel array 400. With reference to FIG. 5, the pixel array 400 may be constructed with the repeating of a unittile (or tile) 400 a in columns and rows. The tile 400 a includessensing pixels 402S and a positioning pixel 402P in its center. Thus,the positioning pixels 402P are repeatedly arranged in the pixel array400. That is, the positioning pixels 402P have a regular pattern.

With reference to FIG. 6 , the pixel array 400 may be constructed withthe repeating of a unit tile 400 b in columns and rows. The tile 400 bincludes sensing pixels 402S and a plurality of positioning pixels 402P.Based on the arrangement of adjacent positioning pixels 402P, thepositioning pixels 402P may be classified in different types ofpatterns. In the illustrated embodiment, the type I pattern comprisestwo adjacent positioning pixels 402P arranged diagonally, the type IIpattern comprises isolated positioning pixels 402P, and the type IIIpattern comprises three adjacent positioning pixels 402P forming atriangle shape. Due to the repeating of the tile 400 b, the differenttypes of patterns of the positioning pixels 402P are also repeatedlyarranged in the pixel array 400. That is, the positioning pixels 402Phave a regular pattern. The different types of patterns of thepositioning pixels 402P provides further enhanced anti-counterfeitingfeatures. For example, the vector comparison may be carried out in thetype I pattern, type II pattern, and type II pattern individually, andthe shifts should pass tests within each of the type I pattern, type IIpattern, and type III pattern. Then, the shifts from each of the type Ipattern, type II pattern, and type III pattern are compared, and shouldbe the same to eventually conclude a match. That is, the vectorcomparison may conclude the same shift ΔV_(type-I) based on the type Ipattern of the positioning pixels 402P, the same shift ΔV_(type-II)based on the type II pattern of the positioning pixels 402P, and thesame shift ΔV_(type-III) based on the type III pattern of thepositioning pixels 402P, and still further, the shifts ΔV_(type-I),ΔV_(type-II), and ΔV_(type-III) should also equal to conclude a match.

With reference to FIG. 7 , the positioning pixels 402P may be randomlydistributed in the pixel array 400. That is, the positioning pixels 402Pmay have a random pattern. Still, adjacent positioning pixels 402P mayform various types of patterns even overall randomly distributed in thepixel array 400. For example, the dashed circle in FIG. 7 highlights twoadjacent positioning pixels 402P in forming a line shape pattern,besides other isolated positioning pixels 402P. The combinationincreases the difficulty of counterfeiting. In various embodiments, suchas in FIGS. 5-7 , the percentage of positioning pixels 402P in the totalamount pixels in the pixel array 400 may range from about 1% to about10%. This range is not trivial. If the percentage of the positioningpixels is below 1%, the anti-counterfeiting feature may not be enhancedsufficiently; if the percentage of the positioning pixels is above 10%,the area of the pixel array may not be sufficiently utilized forfingerprint image capture. In other words, a fingerprint image capturedby the pixel array implementing positioning pixels may have dark pixelin an area percentage of 1% to about 10% of the total area of thefingerprint image.

Besides the positioning pixels, color pixels may be added to a grayscalepixel array to add skin tone information of the fingerprint. Skin toneinformation adds another layer of security beyond comparing minutiapoints of the fingerprints. FIGS. 8A-8G illustrate various embodimentsof adding a plurality of color pixels to an array of otherwise allgrayscale pixels (denoted as “W”). The positioning pixels also help toidentify positions of the color pixels by locating the color pixels nextto the positioning pixels. This helps a software algorithm to quicklyidentify from a fingerprint image where the color pixels locate. Thecolor pixels may also form the same type of pattern as the positioningpixels. With reference to FIG. 8A, three positioning pixels form atriangle shape, and three color pixels of red, green, and blue (RGB) arearranged in the same shape and located next to the positioning pixels.With reference to FIG. 8B, two positioning pixels form a diagonal lineshape, and two color pixels (e.g., RB, GG, or other suitablecombinations) are arranged in the same shape and located next to thepositioning pixels. With reference to FIG. 8C, two positioning pixelsform a horizontal line shape, and two color pixels (e.g., RG, GB, orother suitable combinations) are arranged in the same shape and locatednext to the positioning pixels. With reference to FIG. 8D, twopositioning pixels form a vertical line shape, and two color pixels(e.g., GB, RG, or other suitable combinations) are arranged in the sameshape and located next to the positioning pixels with a column ofgrayscale pixels therebetween. With reference to FIG. 8E, the tile 400 bas discussed above with reference to FIG. 6 is reproduced with addedcolor pixels. The color pixels are added next to the positioning pixelswith the same types of patterns. In the illustrated embodiment, the typeI pattern comprises two adjacent positioning pixels arranged diagonallyand two adjacent color pixels arranged diagonally, the type II patterncomprises isolated positioning pixels with adjacent isolated colorpixels, and the type III pattern comprises three adjacent positioningpixels forming a triangle shape and three adjacent color pixels forminga triangle shape. With reference to FIG. 8F, the color pixels may evenoutnumber the grayscale pixels, and the grayscale pixels outnumber thepositioning pixels. In the illustrated embodiment, the grayscale pixelsonly appear in every other row and every other column with color pixelsfilling remaining pixels not taken by positioning pixels, and thepositioning pixels are randomly distributed or repeatedly distributed.With reference to FIG. 8G, all the sensing pixels in the pixel array maybe color pixels, and the positioning pixels are randomly distributed orrepeatedly distributed. Any other suitable combinations and arrangementsof positioning pixels and color pixels are possible beyond what areillustrated in FIGS. 8A-8G, as will be appreciated by those skilled inthe art.

FIG. 9 shows a flowchart of a method 900 for capturing and recognitionof a fingerprint image from a user's finger illuminated by a displaypanel integrated with an OFPS, according to examples of the disclosure.The method 900 will be described below with references to the exemplaryelectronic device 100 illustrated in FIG. 2 .

At block 902, the method 900 begins with displaying a prompt on thescreen. The screen of the electronic device 100 may be in a lock status.The prompt may be an icon, such as a fingerprint icon or an instructiontext. The prompt highlights a sensing region 108 on the screen. Theprompt is shown by light emitting pixels 222 under the sensing region208. The light emitting pixels 222 can be OLED diodes. The lightemitting pixels 222 outside of the sensing region 108 may be turned offin the lock status or display preset screen saver images.

At block 904, the method 900 detects an input object shown up in thesensing region 108, such as the user's finger 110. The detection may beimplemented by sensing the incident light variation at the opticalsensing elements 207. Alternatively, the display panel 202 may be atouch screen and include touch sensor(s), and the detection may beimplemented by the touch sensor(s). In some applications, the user'sfinger 110 is not necessary to physically touch the top surface 216 ofthe display panel 202. Instead, a near-field imaging can be used forsensing touches detected through a user's glove or other barriers suchas oils, gels, and moisture. When the user's finger 110 stays steady formore than a predetermined time, such as the user holding a finger steadyfor about one hundred milliseconds, the method 900 enters a biometricdetection mode. Otherwise, the method 900 returns to block 902, waitingfor a new user input.

At block 906, the prompt shown on the screen is turned off and the lightemitting pixels 222 under the sensing region 208 start to illuminate theuser's finger 110. The light 270 emitted from the light emitting pixels222 travels through the cover glass 214 and arrives at the user's finger110. The user's finger 110 can include ridges 272 and valleys 274. Theridges 272 of the finger can reflect more light due to a closer distanceto the top surface 216 than the valleys 274, and the valleys 274 canreflect less light. The light 270 is in turn reflected back towards thelight conditioning layer 204.

At block 908, method 400 filters stray light components in the light 270at the collimator 240. With high aspect ratio of the apertures 246, thecollimator 240 only allows light rays reflected from the sensing region108 at normal or near normal incidence to the collimator 240 to pass andeventually reach the image sensing layer 206. The optical sensingelement 207 can be used to measure the intensity of light and convertthe measured intensity into pixel image of the user's finger 110. On theother hand, stray light with a larger angle from normal, strike thecollimator 240, either on its top surface or at surface within theapertures 246 (e.g., aperture sidewalls) and are blocked and preventedfrom reaching the image sensing layer 206 below. The aspect ratio of theapertures 246 is sufficiently large to prevent stray light fromtraveling through the collimator 240, such as from about 5:1 to about50:1. As an example, a light ray reflected from the valley 274 maytravel in a large angel to norm direction and arrive at one sensorelement directly under the ridge 272 in the absence of the collimator240. The image produced by the one sensor element is therefore blurreddue to mixing the lights from regions of the ridge 272 and the valley274. Such a light ray is referred to as stray light. Larger aspectratios of the apertures 246 restrict the light acceptance cone tosmaller angles, improving the optical resolution of the system. In someembodiments, the apertures 246 are cylindrical or conical in shape. Thesidewalls of the apertures 246 may further include grooves or otherstructures to prevent stray light from reflecting off the walls andreaching the OFPS 206 below.

At block 910, the method 900 acquires a fingerprint image at the OFPS206. The sensing pixels 207 in the pixel array of the image sensinglayer 206 convert the incident light into electrical outputs. The pixelarray may comprise sensing pixels that are monochromatic (grayscale)pixels, color pixels, or a combination of monochromatic pixels and colorpixels. The color pixels add skin tone information to the fingerprintimage. The pixel array also includes positioning pixels uniformly orrandomly distributed in the pixel array. Each sensing pixel 207's outputmay correspond to one pixel with grayscale level (or RGB color if colorpixel presented) in the fingerprint image. Each positioning pixel'soutput may correspond to one dark pixel in the fingerprint image. Insome embodiments, each of the sensing pixel may be configured tocorrespond with specific light wavelengths, such as a sensing pixelunder a red light emitting pixel (222R) for sensing a red lightwavelength, a sensing pixel under a green light emitting pixel (222G)for sensing a green light wavelength, and a sensing pixel under a bluelight emitting pixel (222B) for sensing a blue light wavelength.

At block 912, the method 900 acquires vectors representingcharacteristics (minutia points) of a fingerprint with respect tolocations of the positioning pixels. Based on the types of the patternsof the positioning pixels, the vectors may also be classified intodifferent groups, such as a first group of vectors with reference topositioning pixels of a first type of pattern and a second group ofvectors with reference to positioning pixels of a second type ofpattern.

At block 914, the method 900 compares the acquired fingerprint imagewith an authentic reference image previously stored in a memory (or adatabase). The comparison includes comparing the vectors of the twoimages. The comparison of the vectors may be addition to the comparisonof the minutia maps at block 914, adding another layer of security tominutia maps alone. Alternatively, it may be just vectors being comparedat block 914. The vectors might not be the same, as the fingerprint mayshift with respect to the positioning pixels, but the shifts of thevectors should be the same to conclude a match. Further, if the vectorsare classified into different groups (types of patterns), two levels ofcomparisons can be performed. The lower level is to compare vectors andshifts of the vectors in the same group, which should be the same. Thehigher level is to compare vectors and shifts across different groups,which should also be the same to conclude a match. The skin toneinformation can optionally be another criteria to compare in order toconclude a match. If the fingerprint images match, the method 900proceeds to block 916 to unlock the screen. The light emitting pixels222 under the sensing region 108 will stop illumination and join theother light emitting pixels 222 outside of the sensing region 108 tostart display regular desktop icons as in an unlock status. If thefingerprint images do not match, the method 900 proceeds back to block902 to wait for new biometric detection.

Although not intended to be limiting, one or more embodiments of thepresent disclosure provide many benefits to a fingerprint recognitionsystem, such as in consumer (or portable) electronic devices. Forexample, some of the sensing pixels in a pixel array is replaced withpositioning pixels distributed in certain patterns. The positioningpixels provide reference points to identify characteristics of anacquired fingerprint and optionally indicate locations of adjacent colorpixels for providing skin tone information. Anti-counterfeitingcapability of the fingerprint recognition system is further enhanced.

In one exemplary aspect, the present disclosure is directed to an imagesensing apparatus. In some embodiments, the image sensing apparatusincludes a pixel array and a plurality of micro lenses disposed abovethe pixel array. The pixel array includes a plurality of sensing pixelsconfigured to capture minutia points of a fingerprint, and a pluralityof positioning pixels configured to provide positioning codes. In someembodiments, all the sensing pixels are grayscale pixels. In someembodiments, all the sensing pixels are color pixels. In someembodiments, the sensing pixels includes a plurality of grayscale pixelsand a plurality of color pixels. In some embodiments, the color pixelsare positioned adjacent to the positioning pixels. In some embodiments,the color pixels are arranged in a pattern same to a pattern formed bythe adjacent positioning pixels. In some embodiments, the positioningpixels are arranged in a repeated pattern in the pixel array. In someembodiments, the positioning pixels are distributed randomly in thepixel array. In some embodiments, the image sensing apparatus furtherincludes a collimator above the micro lenses and an illumination layerabove the collimator. In some embodiments, the micro lenses are disposeddirectly above the sensing pixels but not above the positioning pixels.

In another exemplary aspect, the present disclosure is directed to anoptical fingerprint sensor. In an embodiment, the optical fingerprintsensor includes an array of light filters arranged in columns and rows,an array of light receiving elements under the array of light filters,where the array of light receiving element is configured to convertincident light reflected from a fingerprint to a fingerprint image, anda plurality of opaque films disposed above a portion of the lightreceiving elements, where the portion of the light receiving elements isconfigured to add dark pixels to the fingerprint image. In someembodiments, the opaque films are made of metal. In some embodiments,the opaque films are disposed between the array of light filters and thearray of light receiving elements. In some embodiments, locations of theportion of the light receiving elements form a regular pattern. In someembodiments, inside the regular pattern, the portion of the lightreceiving elements form at least two different sub patterns. In someembodiments, locations of the portion of the light receiving elementsare distributed randomly. In some embodiments, the array of lightfilters includes a combination of color filters and transparent filters.

In yet another exemplary aspect, the present disclosure is directed to amethod of fingerprint verification. In some embodiment, the methodincludes capturing a fingerprint image by an image sensing device, theimage sensing device including a pixel array of a combination of sensingpixels configured to capture minutia points in the fingerprint image andpositioning pixels configured to provide positioning codes, calculatingvectors of the minutia points with reference to the positioning codes,and comparing the vectors to reference vectors generated from areference fingerprint image to determine a match between the fingerprintimage and the reference fingerprint image. In some embodiments, thevectors include a first group of vectors with reference to a first typeof the positioning codes and a second group of vectors with reference toa second type of the positioning codes. In some embodiments, the methodfurther includes determining shifts between the vectors and thereference vectors and determining whether the shifts are substantiallyequal to determine the match.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An image sensing apparatus, comprising: a pixelarray, the pixel array comprising: a plurality of sensing pixelsconfigured to capture minutia points of a fingerprint; and a pluralityof positioning pixels configured to provide positioning codes; and aplurality of micro lenses disposed above the pixel array.
 2. The imagesensing apparatus of claim 1, wherein all the sensing pixels aregrayscale pixels.
 3. The image sensing apparatus of claim 1, wherein allthe sensing pixels are color pixels.
 4. The image sensing apparatus ofclaim 1, wherein the sensing pixels includes a plurality of grayscalepixels and a plurality of color pixels.
 5. The image sensing apparatusof claim 4, wherein the color pixels are positioned adjacent to thepositioning pixels.
 6. The image sensing apparatus of claim 5, whereinthe color pixels are arranged in a pattern same to a pattern formed bythe adjacent positioning pixels.
 7. The image sensing apparatus of claim1, wherein the positioning pixels are arranged in a repeated pattern inthe pixel array.
 8. The image sensing apparatus of claim 1, wherein thepositioning pixels are distributed randomly in the pixel array.
 9. Theimage sensing apparatus of claim 1, further comprising: a collimatorabove the micro lenses; and an illumination layer above the collimator.10. The image sensing apparatus of claim 1, wherein the micro lenses aredisposed directly above the sensing pixels but not above the positioningpixels.
 11. An optical fingerprint sensor, comprising: an array of lightfilters arranged in columns and rows; an array of light receivingelements under the array of light filters, wherein the array of lightreceiving element is configured to convert incident light reflected froma fingerprint to a fingerprint image; and a plurality of opaque filmsdisposed above a portion of the light receiving elements, wherein theportion of the light receiving elements is configured to add dark pixelsto the fingerprint image.
 12. The optical fingerprint sensor of claim11, wherein the opaque films are made of metal.
 13. The opticalfingerprint sensor of claim 11, wherein the opaque films are disposedbetween the array of light filters and the array of light receivingelements.
 14. The optical fingerprint sensor of claim 11, whereinlocations of the portion of the light receiving elements form a regularpattern.
 15. The optical fingerprint sensor of claim 14, wherein insidethe regular pattern, the portion of the light receiving elements form atleast two different sub patterns.
 16. The optical fingerprint sensor ofclaim 11, wherein locations of the portion of the light receivingelements are distributed randomly.
 17. The optical fingerprint sensor ofclaim 11, wherein the array of light filters includes a combination ofcolor filters and transparent filters.
 18. A method of fingerprintverification, comprising: capturing a fingerprint image by an imagesensing device, the image sensing device including a pixel array of acombination of sensing pixels configured to capture minutia points inthe fingerprint image and positioning pixels configured to providepositioning codes; calculating vectors of the minutia points withreference to the positioning codes; and comparing the vectors toreference vectors generated from a reference fingerprint image todetermine a match between the fingerprint image and the referencefingerprint image.
 19. The method of claim 18, wherein the vectorsinclude a first group of vectors with reference to a first type of thepositioning codes and a second group of vectors with reference to asecond type of the positioning codes.
 20. The method of claim 18,further comprising: determining shifts between the vectors and thereference vectors; and determining whether the shifts are substantiallyequal to determine the match.